It is known to position a sample such that an electromagnetic beam from a source thereof is caused to interact with said sample, and enter a detector. Change in intensity and/or polarization state of the beam is then analyzed to provide insight to the sample's optical and physical characteristics.
It is also known to place the source and detector on effective arms which operate on a 2θ basis, such that when the angle of incidence of a beam onto a sample is set at θ with respect to a perpendicular to the sample surface, the detector is also set at an angle θ, (reflected through the perpendicular locus), so that a beam reflecting from the sample enters thereinto. A problem can develop where the angles of incidence (AOI) and angle of reflection (AOR) both approach 0 degrees, (ie. both project near 0.0 degrees to a perpendicular to the sample surface), in that physical aspects of the effective arms, source and detector can limit motion. This is especially true when a camera, which is used to provide an optical view of sample during investigation by the electromagnetic beam, is positioned at an offset from the sample along a perpendicular to the surface thereof, as the camera is then often positioned so as to even further limit source and detector motion than otherwise is the case. Conventional thinking, however, is that such a camera must be positioned offset from a sample surface along a perpendicular thereto, as otherwise the image provided thereby will not be in focus over the full area of the sample.
Known prior art includes:
A Patent to Liphardt, U.S. Pat. No. 7,567,345 which describes applying a Scheimpflug condition to a source and/or detector in an ellipsometer system.
A Patent to Horie, U.S. Pat. No. 7,095,498 describes the presence of a pinhole mirror in a spectroscopic ellipsometer system. The pinhole mirror is rotated so that a beam of electromagnetic radiation is oriented along a locus which is oblique angle, rather than along a normal thereto;
A Patent to Masao, U.S. Pat. No. 5,963,326 describes an imaging ellipsometer which uses a large cross-section measuring beam rather than a small beam spot as is the focus in the present invention;
A Patent to Finarov, U.S. Pat. No. 5,517,312 mentions the Scheimpflug condition in the context of a scanning ellipsometer wherein a beam is scanned over a sample and a pattern recognition camera which is designed to utilize the Scheimpflug condition is applied;
The prior art does not, to the Inventor's knowledge, describe applying the Scheimpflug condition to design of reflectometer, ellipsometer, polarimeter or the like systems, where camera elements, which provide a view of the sample surface, are configured to meet the Scheimpflug condition.